Phorbol esters and cytokines regulate the expression of the NEMO-related protein, a molecule involved in a NF-kappa B-independent pathway

The NF-kappa B signaling pathway plays a crucial role in the immune, inflam matory, and apoptotic responses. Recently, we identified the NF-kappa B Ess ential Modulator (NEMO) as an essential component of this pathway. NEMO is a structural and regulatory subunit of the high molecular kinase complex (I KK) responsible for the phosphorylation of NF-kappa B inhibitors. Data base searching led to the isolation of a cDNA encoding a protein we called NRP (NEMO-related protein), which shows a strong homology to NEMO. Here we show that NRP is present in a novel high molecular weight complex, that contain s none of the known members of the IKK complex. Consistently, we could not observe any effect of NRP on NF-kappa B signaling. Nonetheless, we could de monstrate that treatment with phorbol esters induces NRP phosphorylation an d decreases its half-life. This phosphorylation event could only be inhibit ed by K-252a and stauroporin. We also show that de novo expression of NRP c an be induced by interferon and tumor necrosis factor cy and that these two stimuli have a synergistic effect on NRP expression. In addition, we obser ved that endogenous NRP is associated with the Golgi apparatus. Analogous t o NEMO, we find that NRP is associated in a complex with two kinases, sugge sting that NRP could play a similar role in another signaling pathway.